Foundation performance requirements Flashcards
Foundations has the following function
1-Transfer the loads without failing of the soil, for example choosing a spread footing will have high stress on soil which will lead to failure of the soil , thus choosing instead a raft/mat foundation
2- Transfer loads to underlying ground without excessive settlement
2-Transfer loads to underlying ground without differential settlement
The actual loads on the foundation are calculate by Structural Engineer
True
However we have rule of thumbs such as
Each 1 m2 of one floor weighs between 1 to 2 tons , then u get tributary area of each column and multiply by number of floors then u will find pressure
Nominal load ( It is the load that we use in design , which is a conservative estimate)
true
We have two design methods that we use
ASD; Allowable stress design method
LRFD: Load and resistance Factor Design method
In ASD (allowable stress design method )
We have one general factor
First i get the nominal load , then i will need the foundation capacity to be greater than a factor of safety multiplied by nominal load
In load and resistance factor design method
Since the uncertainty present between the resistance and the loads is different , then why shall we use one factor only.
In load and resistance factor design method we apply factors for the loads ( for example for dead loads 1.2, for live loads 1.4, for environmental 1.6) and for the resistance capacity of the soil (factors like 0.7,0.8, 0.9 it depends on what soil conditions we have)
WE are trying not to overdesign
In Foundationperformance we have allowable settemnet
To get the max allowable setltement , it is easy , we have the angular distotion from a table
The angular distortion divided by the settlement ; must be equal to the agular sitaortion for allowable settlement of 2.5 cm over an allowable settlement of 2.5.
Depending on the type of structure and soil u will get that angular distortion
